From pre-Grimm *petwṓr, with an irregular consonant change from *kʷetwṓr, the neuter form of Proto-Indo-European *kʷetwóres. The consonant change was probably caused by the influence of the p- in "five".
*fedwōr (ordinal *fedurþô)
Note: The declension for all three genders is identical.
In North and West Germanic, the form lost its -d- and became *fewōr, *feur, from which the attested forms are descended. In Old Norse, this would have given *fjór, but plural adjective endings were then added to this form.
- Old English: fēower
- Old Frisian: fiūwer
- Old Saxon: fiuwar, fiwar, fior
- Old Dutch: *viuwar (found in toponym Uiuuuarflet now called Viervliet), *fior, fier
- Old High German: fior
- Old Norse: fjórir
- Gothic: 𐍆𐌹𐌳𐍅𐍉𐍂 (fidwōr)
- Crimean Gothic: fyder